A semiconductor device for handling high power is generally referred to as a power device. In order to handle high power, the semiconductor device is desired to achieve a higher withstand voltage and lower loss and to enable use thereof in an environment at a high temperature and the like. Therefore, silicon carbide (SiC) has recently increasingly been adopted as a material for forming a semiconductor device. SiC is a wide-bandgap semiconductor greater in bandgap than silicon (Si) that has conventionally widely been used as a material for forming a semiconductor device. Therefore, by adopting SiC as a material for forming a semiconductor device, a higher withstand voltage, a lower ON resistance and the like of a semiconductor device can be achieved. In addition, a semiconductor device adopting SiC as a material is also advantageous in that lowering in characteristics when used in an environment at a high temperature is less likely than in a semiconductor device adopting Si as a material.
Among power devices in particular, a vertical SiC-MOSFET high in switching speed and high in conversion efficiency in a low voltage region is effectively made use of as a semiconductor device for large machinery requiring particularly high switching characteristics, such as electric power conversion equipment used, for example, for a hybrid car.
In adopting SiC as a material for a semiconductor device, however, it is not easy to form ohmic contact low in contact resistance between an n-type region, a p-type region and an electrode formed in contact with the n-type region or the p-type region, as compared with an example where Si is adopted as a material for a semiconductor device. Specifically, for example in a case where Si is adopted as a material for a semiconductor device, in forming an electrode, for example, Al (aluminum) is used and heat treatment at a relatively low temperature is performed. By doing so, Si and Al establish good ohmic contact with each other. If SiC is adopted as a material for a semiconductor device, however, it is more difficult to form ohmic contact than in the case where Si is adopted as a material for a semiconductor device described above.
Therefore, in adopting SiC as a material for a semiconductor device, for example, a joint method in which, while Ni (nickel) and SiC are brought in contact with each other, they are subjected to heat treatment at a relatively high temperature (for example, approximately 1000° C.) has conventionally been used. Namely, by performing heat treatment as described above, Ni and Si atoms in SiC are alloyed. As a result of this alloying, Ni and SiC establish good ohmic contact. Thus, it has been known that contact resistance can be lowered by adopting Ni (nickel) as a material for an electrode in contact with an n-type SiC region containing an n-type impurity (an impurity having an n conductivity type) and adopting Ti (titanium)/Al (aluminum) as a material for an electrode in contact with a p-type SiC region containing a p-type impurity (an impurity having a p conductivity type) (see, for example, Satoshi TANIMOTO et al., “Practical Device-Directed Ohmic Contacts on 4H—SiC,” IEICE Transactions C, the Institute of Electronics, Information and Communication Engineers, April 2003, Vol. J86-C, No. 4, pp. 359-367 (Non-Patent Document 1)).